Fluid pump with a flexible toothed belt

ABSTRACT

A fluid pump includes a fluid-tight housing containing two spaced, externally-toothed pulley wheels, an internally-toothed drive belt that wraps around and engages the teeth of the two pulley wheels and moves as they rotate, and a guide block in the space between the two pulley wheels. The housing includes a fluid outlet port adjacent where the drive belt engages a first of the two pulley wheels to discharge fluid pressed out from between the teeth of the drive belt, and a fluid inlet port adjacent where the drive belt disengages from the first pulley wheel. The guide block defines a first face that extends with the drive belt to a nip where the drive belt engages the first pulley wheel and a second face that includes a first portion which extends from the first face in an arc around the periphery of the first pulley wheel and a second portion which extends away from the periphery.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a fluid pump, and is particularly, althoughnot exclusively, useful for the self-priming pumping of liquids.

Gear pumps are known which entrain fluid into the mesh of twocounter-rotating cogs and expel the fluid under pressure, but such gearpumps need fast rotation of the gears and require to be manufacturedwith close tolerances.

The present invention overcomes or mitigates these drawbacks of the gearpump. The present invention provides a fluid pump comprising aninternally-toothed drive belt drivingly coupled to a correspondinglyexternally-toothed first pulley wheel and arranged over a belt guide,which preferably takes the form of a second pulley wheel, spaced fromthe perimeter of the first pulley wheel, a fluid-tight housingcontaining the drive belt and pulley wheel, and means for coupling themotion of the first pulley wheel and the drive belt to that of anexternal drive; the housing having a fluid inlet port communicating witha space between the pulley wheels and the belt guide, and a fluid outletport closely adjacent the region at which the drive belt engagestangentially with the first pulley wheel with their respective teeth inpartial engagement; whereby motion of the first pulley wheel causesfluid from the space between the pulley wheel and the belt guide to bedrawn into the nip of the first pulley wheel and the drive belt and thento be expelled under pressure to the fluid outlet port.

The invention also provides,a pumping system comprising a main fluidpump and a pump according to the invention used as a primer for the mainfluid pump.

The fluid pump of the invention has been found surprisingly to pump withgreat efficiency even at low rotational speeds; whilst the gap betweenthe drive belt and the housing is important, there is still a reasonabledegree of manufacturing tolerance allowed, and the fluid pump can bemass produced from plastics materials with great economy.

In order that the invention may be better understood, preferredembodiments thereof will now be described, by way of example only, withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation of a first embodiment of the invention, butwith a front closure plate removed for greater clarity;

FIG. 2 is a top plan of the fluid pump of FIG. 1, including the frontclosure plate;

FIG. 3 and FIG. 4 are respectively left-hand and right-hand elevationsof the fluid pump of FIGS. 1 and 2;

FIG. 5 is a rear elevation of the fluid pump of FIGS. 1-4; and

FIG. 6 is a front elevation of a modification, as a second embodiment ofthe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 to 5 of the accompanying drawings, a firstembodiment of the invention consists of a fluid pump 10 for pumpingeither air or another gas, or else a liquid such as a hydrocarbon or anaqueous liquid. The fluid pump may be used in an extremely wide range ofapplications, including for example as a fuel injection pump and as aprimer for a larger pump. It is self-priming.

In this example, the fluid pump 10 has a box-shaped housing 20 with afront plate 23 removably secured thereto by screws (not shown). Thespace within the housing 20 is sealed from the exterior throughout bydouble track seals, and one example of this is shown between the housing20 and the front plate 23, in the form of an O-ring 19.

The housing contains two identical spaced toothed pulley wheels 11, 12mounted for rotation in a common plane on pins 13, 14 respectively. Thepulley wheels mesh with an internally-toothed flexible drive belt 16,and rotate in the same direction 17. At least half of the space betweenthe pulley wheels 11, 12 is taken up by a fluid guide block 15 which isas wide as the drive belt 16. As shown in FIG. 1, the guide block 15 hasfirst faces 15 a, 15 b which define the lengthways path of the drivebelt 16 between the pulley wheels. Second faces 21, 22 include arcuatefirst portions 21 a, 22 a which follow closely the path of the teeth ofthe respective pulley wheels into the nip between the drive belt 16 andeach respective pulley wheel 11, 12. The first portions join the firstfaces 15 a, 15 b. Second portions 21 b, 22 b, which are shown as beingflat, extend from the first portions away from the peripheries of thepulley wheels 11, 12.

The space between the pulley wheels 11, 12 communicates with a fluidsource (not shown), i.e. with the pump inlet, by symmetrically-arrangedfluid inlet ports 31, 32 and inlet pipes 31 a, 32 a connectedrespectively thereto. In this example, the inlet ports 31, 32 are on therear of the fluid pump only, but another pair of fluid inlet ports couldof course be arranged opposite those fluid ports, at the front side ofthe fluid pump.

As indicated above, fluid in the space between the pulley wheels 11, 12is entrained by the teeth of the pulley wheels, and guided by the guideblock 15, to enter the region at which the pulley wheel teeth mesh withthe drive belt 16. The fluid is compressed by the meshing action of theteeth, as the internal teeth of the drive belt enter into thecorrespondingly-recessed portions between teeth of the pulley wheels 11,12. In this example, the teeth are of a constant cross section acrossthe width of the belt. In this particular example, in fact, the drivebelt has an HTD profile, and has an 8 mm pitch with a 30 mm width: thepulleys are also of the HTD standard. However, any configuration of beltand pulley wheel which allows intermeshing with an associated fluidexpulsion would suffice and could be substituted as appropriate todifferent engineering requirements.

One of the toothed pulley wheels could be replaced by a non-toothed one,or even simply by a stationary belt guide sufficient to keep the belt onits path around the first pulley wheel within the sealed housing.

I have discovered that the fluid is pumped by the intermeshing teeth,and that the gap between the housing and the belt and pulley, at leastin the intermeshing region, is such as to cause the fluid to be expelledtransversely, i.e. normal to the plane of the pulley wheels and drivebelt. For this reason, outlet ports are disposed in two pairs, over therespective regions at which the drive belt engages tangentially with thefirst and second pulley wheels with their respective teeth in partialengagement. In this example, the two pairs of outlet ports are allcylindrical. A first pair 35, 37 is arranged adjacent the upper pulleywheel 11, with one outlet port 35 at the rear and the other outlet port37 at the front, facing in mutually opposite directions. At thecorresponding position over the second pulley wheel 12, outlet ports 34and 36 are also disposed on opposite sides of the pulley wheel. In eachcase, the diameter of the outlet port is approximately 1.5 times thespacing between adjacent teeth of the pulley wheel 11. However, theoutlet ports do not have to be cylindrical, and they could for examplebe slot-shaped or arcuate. Their overall length, following the path ofthe pulley wheel teeth, is preferably in the range of 1 to 4 times thespacing of the teeth, and advantageously even between 2 and 4 times thespacing, the greater length tending to reduce the back pressure andhence the unwanted hydraulic braking.

In this example, the outlet ports at the rear communicate with bores inthe housing 20 which exit the housing on its left and right-hand sides,as shown most clearly in FIG. 2. The outlet ports 34-37 communicaterespectively with outlet pipes 34 a-37 a.

The pulley wheels, 11, 12 are driven by an external prime mover (notshown) such as an electric motor through appropriate gearing. In thisexample, the prime mover is drivingly coupled to the lower pulley 12through a spindle 24 on the axis of the pulley.

The gap between the outer smooth surface 18 of the drive belt 16 and theinner surface of the housing is fairly constant and is sufficientlynarrow to restrict fluid flow, yet sufficiently wide to allow relativemovement. Preferably the gap is in the range of 0.1-2 mm. The gap isparticularly important in the region of the outlet ports.

In the alternative examples where there is only one toothed pulleywheel, clearly there would only be one nip region to use as the pumpfluid outlet.

Clearly the efficiency of the pump, the velocity ratios and mechanicaladvantages and other relevant parameters will be selected by appropriatedesign, to suit the pumping requirement. For the pumping of fluids, Ihave found that it is advantageous to set the width of the drive belt inthe range of 0.1-0.5 times the radius of the pulley wheel. For greatestefficiency, I have found it ideal to have the two pulley wheels equal insize, but this is not essential, and neither is it essential for thesecond pulley wheel to be toothed, if the second pair of outlets is notrequired. Further, while two pulleys are provided in this example, adifferent number could function satisfactorily.

In the preferred example, the belt is of polyurethane, although otherplastics materials are envisaged. It is of course important that thedrive belt should be of an impervious material, when liquids are to bepumped. Again, in this example, the pulley wheels are of nylon(registered trade mark) or other thermoplastics compounds, and the pins13, 14 are of stainless steel, the housing 20 being of aluminium and thefront plate 23 of perspex, but for mass production it is envisaged thatan all-plastics assembly would be appropriate and would offer greatesteconomy. Different plastics materials may be used for differentcomponents.

The pump illustrated in FIGS. 1 to 5 has been driven at 150 rpm, and atthis speed it developed a pressure differential of 0.8 bar, pumpingwater at 7.5 litres per minute, with an internal pressure of greaterthan about 20 bar (300 psi). To achieve this pumping action, the pumpwas driven by a 380 watt electric motor.

A second embodiment of the invention will now be described withreference to FIG. 6, which shows a variant of the first embodiment in aview corresponding to FIG. 1.

Instead of the guide block 15, there are two guide blocks 1,3 followingpart of the periphery respectively of pulley wheels 11 and 12 which aredriven in the directions 4 and 2. This leaves more open space in theregion between the pulley wheels.

What is claimed is:
 1. A fluid pump comprising an externally-toothedfirst pulley wheel; a second pulley wheel spaced from a periphery of thefirst pulley wheel; an endless internally-toothed drive belt drivinglycoupled to and wrapped around the externally-toothed first pulley wheeland the second pulley wheel; a fluid-tight housing containing the drivebelt and the first and second pulley wheels; means for coupling themotion of the first and second pulley wheels and the drive belt to thatof an external drive; a fluid inlet port in the housing communicatingwith a space between the first pulley wheel and the second pulley wheel;a fluid outlet port closely adjacent a region where the drive beltengages tangentially with the first pulley wheel with their respectiveteeth in partial engagement; and a guide block located within the spacebetween the first pulley wheel and the second pulley wheel, the guideblock having a first face adjacent a portion of the belt which in useapproaches the fluid outlet port, and a second face adjacent the portionof the first pulley wheel which in use, approaches the fluid outletport, wherein the first and second faces of the guide block meet at apoint which is closer to a location where the drive belt comes into meshwith the first pulley wheel than the distance between a location wherethe belt comes out of mesh with the first pulley wheel and the nearestportion of the second face of the guide block, said second face of theguide block including a first portion which extends from the first facein an arc around the periphery of the first pulley wheel, and a secondportion which extends from the first portion away from said periphery,whereby motion of the first pulley wheel causes fluid from the spacebetween the first pulley wheel, the second pulley wheel, and the guideblock to be drawn into a nip between the first pully wheel and the drivebelt and then to be expelled under pressure to the fluid outlet port. 2.A fluid pump according to claim 1, wherein the drive belt has a width inthe range of 0.1-0.5 times the radius of the first pulley wheel.
 3. Afluid pump according to claim 1, wherein the drive belt is of a plasticsmaterial and/or the housing and pulley wheels are of a plastics materialor of respective different plastics materials.
 4. A fluid pump accordingto claim 1, wherein said second portion of said guide block is flat. 5.A fluid pump according to claim 1, wherein the housing and drive belthave therebetween, for at least a portion of the belt path around thenip of the first pulley wheel and the drive belt, a narrow gapsufficiently wide to allow relative movement but sufficiently narrow torestrict fluid flow, and the fluid outlet port, where it communicateswith the space between the first pulley wheel and the drive belt lieswholly within the area defined by the outer surface of the drive belt.6. A fluid pump according to claim 5, wherein the said narrow gap is inthe range of 0.1-2.0 mm.
 7. A fluid pump according to claim 1, whereinthe fluid outlet port faces one side of the first pulley wheel so thatit receives fluid expelled transversely thereof, generally normal to theplane of rotation of the drive belt and pulley wheels.
 8. A fluid pumpaccording to claim 7, wherein a further fluid outlet port is locatedtransversely opposite the said fluid outlet port so that it receivesfluid expelled transversely in the opposite direction to the fluidexpelled through the said fluid outlet port.
 9. A fluid pump accordingto claim 1, wherein the housing has an additional fluid outlet port overthe region at which the drive engages tangentially with the secondpulley wheel with their respective teeth in partial engagement.
 10. Afluid pump according to claim 9, wherein the housing has a still furtherfluid outlet port transversely opposite said additional fluid outletport so that it receives fluid expelled transversely in the oppositedirection.
 11. A fluid pump according to claim 1, wherein the fluidoutlet port is as wide as between 1 and 4 times the spacing of the teethof the first pulley wheel.
 12. A fluid pump according to claim 11,wherein said width of the outlet port corresponds to the width ofbetween two and four teeth of the first pulley wheel.